The sine-squared potential is introduce to describe the interaction between particles and the crystal.The motion equation of the planar channelling particles is reduced to the pendulum equatione by this interaction potential.The solution of the equation and the period of the particle motion are expressed exactly by means of Jacobian elliptic function and elliptic integral.The radiation intensity and properties of the radiation spectrum are discussed.It is point out that it is possible to take channeling radiation as a new γ-Laser.